Work on resetting in baroreceptors form normotensive (NTR) and spontaneously hypertensive rats (SHR) is in progress. We have demonstrated that the resetting is unrelated to steady-state changes in the compliance of hypertensive vessel walls and that it is probably unrelated to alterations in the intrinsic properties of the baroreceptors themselves. Attention is directed, therefore, to coupling mechanisms and to destruction of low threshold baroreceptors. The sodium sensitivity of baroreceptors is under study and its role in body fluid volume and body sodium regulation is being examined. Ionic sensitivity in general is now being tested. The dynamic properties of NTR and SHR baroreceptors and NTR and SHR aortae are under study. BIBLIOGRAPHIC REFERENCES: Tuley, F.H., A.M. Brown and W.R. Saum. 1977. Response characteristics of aortic baroreceptors elicited by broad-band ("white noise") pressure stimuli. Biophysical J. 17: 18a. Kunze, D.L., W.R. Saum and A.M. Brown. 1977. Role of sodium-sensitive baroreceptor reflexes in the regulation of blood pressure and body fluid volume. Fed. Proc. 36: 487.